Known copolymers comprising aromatic polyester and lactone therein are limited to those formed from aromatic polyester having intrinsic viscosities ("IV") which are low and melt viscosities ("MV") which are low. Japanese Patent Publication 4115 published Feb. 5, 1973 ("Publication 4115") teaches the use of aromatic polyesters such as poly(ethylene terephthalate) ("PET") and poly(butylene terephthalate) ("PBT"). Publication 4115 has Examples illustrating PET's use in a copolymer wherein the PET has a number average molecular weight ("M.sub.n ") of 500-5,000 which corresponds to an IV of less than 0.3 as measured in a 60/40 by weight mixture of phenol and tetrachloroethane solvents according to William L. Hergenrother and Charles Jay Nelson, "Viscosity-Molecular Weight Relationship for Fractionated Poly(ethylene Terephthalate)", Journal of Polymer Science 12, 2905-2915 (1974). These low M.sub.n and low IV PETs also have low melt viscosities, i.e., less than 100 poises at 280.degree. C., according to Andrzej Ziabicki, "Effects of Molecular Weight on Melt Spinning and Mechanical Properties of High-Performance Poly(ethylene Terephthalate) Fibers", Textile Res. J. 66(11), 705-712 (1996). The Ziabicki article uses data from A. Dutta, "Identifying Critical Process Variables in Poly(ethylene Terephthalate) Melt Spinning", Textile Res. J. 54, 35-42 (1984) which teaches that rheological studies of the shear viscosity of PET indicate that PET behaves like a Newtonian liquid for shear rates up to about 200/seconds. Publication 4115 teaches that even when using such low IV and MV PET, at least 50 weight percent .epsilon.-caprolactone is still required in order to plasticize PET melt and then mix with PET.
Publication 4115 also has an Example illustrating PBT's use in a copolymer wherein the PBT has a M.sub.n of 1,200 which corresponds to an IV of less than 0.1 as measured in a 60/40 by weight mixture of phenol and tetrachloroethane solvents according to W. F. H. Borman, "Molecular Weight-Viscosity Relationships for Poly(1,4-butylene Terephthalate)", Journal of Applied Polymer Science 22, 2119-2126 (1978). This low M.sub.n and low IV PBT also has a low melt viscosity, i.e., less than 10 poises at 250.degree. C., according to the Borman article and the melt viscosity of PBT is Newtonian at low shear stress, i.e. shear rates equal to or less than 100/seconds.
Publication 4115 also teaches an initial reaction between both ends of an aromatic polyester, P, with .epsilon.-caprolactone, L, and then reacting the oligomeric L-P-L with a polyfunctional acylation agent, A to form multiblock copolymer -L-P-L-A-L-P-L-A-L-P-L- in order to extend the chain and obtain high molecular weight polymers which are suitable for use as thermoplastic elastomers. Publication 4115 teaches that the use of a polyfunctional acylation agent results in the preceding regular repeating structure.
Known process for making the foregoing copolymers involve the use of an autoclave or reactor with a stirrer and a nitrogen atmosphere by reaction of oligomeric polyester with .epsilon.-caprolactone at reaction times of at least two hours. Japanese Patent Publication 4116 published Feb. 5, 1973 ("Publication 4116") and Kokai Patent Publication 157117 published Sep. 6, 1984 ("Publication "157117") teach Example reaction times of 2-5 hours. The inventors of Japanese Patent Publication 49037 published Dec. 14, 1977 ("Publication 49037") acknowledge that its prior process, as disclosed in Publication 4116, results in ester interaction between the aromatic polyester and polycaprolactone blocks and thus, the copolymer's block length was short and the copolymer melting point was low. Publication 49037 teaches that to overcome the preceding problem, that the reaction temperature needs to remain below the aromatic polyester's melting point, i.e. solid state polymerization, so that the aromatic polyester powder remains in a solid state throughout the reaction; unfortunately, as a result, each Example teaches a very long reaction time of 24 hours.
Example 1 of Publication 4116 teaches that at least 50 weight percent .epsilon.-caprolactone is required in order to plasticize higher IV PET (M.sub.n =20,400; IV.ltoreq.0.67) and then mix with it. Example 5 of Publication 4116 teaches that at least 50 weight percent caprolactone is required in order to plasticize higher IV PBT (M.sub.n =10,500; IV.ltoreq.0.4) and then mix with it. These extensive mixing results in increased transesterification.
The inventors of Japanese Patent Publication 27268 published May 11, 1992 ("Publication 27268"); Kokai Patent Publication 57302 published Aug. 23, 1993 ("Publication 57302"); Kokai Patent Publication 253764 published Sep. 9, 1992 ("Publication 253764"); Kokai Patent Publication 264156 published Sep. 18, 1992 ("Publication 264156"); and U.S. Pat. Nos. 4,584,353 and 4,670,510 recognized the deficiencies in the processes of Publications 4115, 4116, and 49037 by stating that the obtained viscosity was low and thus, the applications were limited.
Publications 27268 and 57302 and U.S. Pat. Nos. 4,500,686; 4,584,353; 4,670,510; and 4,670,948 teach that a block copolymer of PBT and polycaprolactone may be formed according to Publication 4116, i.e, the block copolymer was formed in a reaction vessel under nitrogen gas and stirring at 230.degree. C. for 2 hours. The unreacted .epsilon.-caprolactone was removed from the melt and the block copolymer was then mixed with additional PBT and epoxy at room temperature and then the mixture was extruded at 230.degree. C. to form multiblock copolymers. Pre-mixing PBT and .epsilon.-caprolactone in long reaction times results in increased transesterification which is unacceptable. They also teach that the block copolymer must be mixed with pure PBT in order to achieve desired mechanical properties.
A catalyst may be used in the foregoing reaction of PBT and .epsilon.-caprolactone in a stirrer apparatus as taught by Publications 253764 and 264156 wherein the catalyst was monobutyl monohydroxy tin oxide and the reaction time was 30 minutes. These publications also teach blending epoxy and 5-valenced phosphorus compound with the oligomeric copolymer in order to improve the molecular weight.
Because known oligomeric copolymers are made from starting aromatic polyesters having low IV and MV, known oligomeric copolymers have low IV and MV. Known oligomeric copolymers and resulting multiblock copolymers also have short block lengths and high transesterification because the processes for making them have a long residence time. As a result, fibers which are spun from the foregoing copolymers are undesirable because the fibers have low crystallinity, low melting points, low ultimate tensile strength, and undesired stress/strain behavior.
It would be desirable to have a diblock copolymer wherein the starting aromatic polyester has a high IV, the copolymer block length is long, the transesterification degree is low, the reaction time for making the copolymer is short (minutes instead of hours), and the use of a polyfunctional acylation agent is not required to extend the chain. We tried to accomplish the foregoing by using a reactor with a stirrer to make a diblock copolymer from starting aromatic polyester having a higher IV and melt viscosity than that taught in the prior art but this attempt was unsuccessful as described below in the Comparative Example because an autoclave does not allow mixing between high IV PET and .epsilon.-caprolactone wherein the amount of .epsilon.-caprolactone is less than 50 percent by weight based on the diblock copolymer weight.